It can support more but not officially. If you're into overclocking, you can always try to keep the memory in sync with the HT link thus raising the speed above 400MHz. If you're not into overclocking, then as the Don says, PC3200 (200MHz / 400DDR) is the max.
I figured as much but wanted to check. Not really into overclocking, have done it in the past but have no need at the mo coz does everything well at standard settings.